The present invention relates to a plate mounting apparatus for a printing press, wherein one end of a plate is gripped by one fixing unit arranged in a gap in an outer circumferential surface of a plate cylinder, the plate is wound around the outer circumferential surface of the plate cylinder, and the other end of the plate is gripped by the other fixing unit to mount the plate on the plate cylinder, and an old plate is removed from the plate cylinder upon a change in specifications of printed matters and a new plate is mounted in place of the old plate.
A gap having almost a rectangular section and a length almost equal to the overall length of a plate cylinder is formed in the outer circumferential surface of the plate cylinder for a sheet-fed printing press. A plate lockup apparatus consisting of a leading-side lockup device serving as a fixing unit for fixing one end of a plate and a trailing-side lockup device serving as a fixing unit for fixing the other end of the plate is axially fixed on the bottom surface of the gap.
Each of the conventional leading- and trailing-side lockup devices comprises an elongated lockup table extending in the axial direction of the plate cylinder, a plurality of gripper plates, swingably supported at an edge portion of this lockup table by a plurality of bolts, for gripping or releasing the plate with or from the lockup table, and a plurality of cams which can be respectively engaged with gaps at the edges of the gripper plates. The plurality of cams are pivotally aligned along the axis. A plurality of compression coil springs are interposed between the lockup table and the gripper plates to bias the gripper plates in an open direction.
With the above arrangement, in order to mount a plate on a plate cylinder, when a cam shaft of the leading-side lockup device is pivoted, the gripper plates which are divided in the axial direction of the plate are released upon disengagement from the cams and are simultaneously opened by the elastic forces of the compression coil springs. An end of the plate is inserted between the leading-side lockup device and the corresponding lockup table. When the cam plate is pivoted in the direction opposite to the direction described above, the gripper plates are pivoted against the elastic forces of the compression coil springs by the behavior of the cams and are closed, thereby gripping the leading edge of the plate.
Another conventional apparatus is disclosed in Japanese Patent Laid-Open No. 1-127346. In this apparatus, the lockup tables and the gripper plates are disposed in the radial direction of a plate cylinder so that a trailing-side gripper surface of the plate conventionally formed in the circumferential direction of the plate cylinder is formed in the radial direction of the plate cylinder. The edge of the plate is bent at a right angle by an external bending machine. With this arrangement, after the leading edge of the plate is gripped, the bent portion of the trailing edge portion of the plate wound around the circumferential surface of the plate is inserted between the lockup tables and the gripper plates. The gripper plates are swung by a cam mechanism to grip the bent portion of the plate. The trailing-side lockup device as a whole is circumferentially moved to uniformly mount the plate, thereby bringing the plate into tight contact with the surface of the plate cylinder.
In such a conventional press, when an old plate is replaced with a new plate due to changes in contents of printed matters, the trailing-side cam shaft is pivoted to open the trailing-side lockup device. One end of the plate which is released from gripping is kept held, and the plate cylinder is rotated. The leading-side cam shaft is pivoted to open the leading-side lockup device to release the other end of the plate from gripping, thereby removing the old plate. Thereafter, opening/closing of the plate lockup devices and the pivotal operation of the plate cylinder are repeated to mount the new plate. In plate replacement, however, pivotal movement of the cam shaft and rotation of the plate cylinder must be performed manually or upon operation of a push button. Plate replacement is cumbersome and requires skills since the old and new plates must be manually held.
As disclosed in Japanese Patent Laid-Open No. 62-169647, a plate removal apparatus is proposed wherein a suction pad supported on a support member is brought to come close to a plate cylinder and to chuck an end of a plate to remove the plate.
In such a conventional plate mounting apparatus for mounting a plate on a plate cylinder, it is difficult to insert a plate into a narrow opening of the leading-side plate lockup device, thus resulting in time-consuming, cumbersome operations. Since the plate guided toward the trailing-side lockup device is not brought into tight contact with the circumferential surface of the plate cylinder, it is difficult to insert the trailing end bent at almost a right angle into the opening of the trailing-side plate lockup device, thus requiring a more time-consuming, cumbersome operation and much labor.
A plate supply apparatus for supplying a plate to a plate cylinder is proposed, as disclosed in Japanese Patent Laid-Open No. 58-187355 or the like. This plate supply apparatus comprises an arm having a suction pad fixed at its distal end portion. A plate mounting leading-side hook and a plate mounting trailing-side hook are mounted in the plate cylinder.
When a plate is mounted on the circumferential surface of the plate cylinder by using the plate supply apparatus described above, the arm having the suction pad which chucks the plate is moved between a plate mounting position and the leading-side hook in the circumferential portion of the plate cylinder to hook one bent portion of the plate against the leading-side hook. The plate is then wound around the circumferential surface, and the other bent portion of the plate is hooked against the trailing-side hook.
In an apparatus for manually attaching/detaching a plate of all the conventional plate mounting apparatuses, however, it is difficult to insert a plate into the narrow opening of the leading-side plate lockup device, thus requiring time-consuming, cumbersome operations and much labor. In addition, since the plate guided to the trailing-side plate lockup device is not brought into tight contact with the circumferential surface of the plate cylinder while being wound around the plate cylinder, it is difficult to insert the trailing end of the plate which is bent at almost a right angle into the opening of the trailing-side plate lockup device, thus requiring a more time-consuming, cumbersome operation and much labor.
In the apparatus for chucking the end of the plate by the suction pad, the structure becomes complicated, and a suction error tends to occur, thus failing to assure safety and reliability.
As described above, in the apparatus for hooking the bent portion of the plate against the hooks in the plate cylinder, it is difficult to bring the plate into tight contact with the circumferential surface of the plate cylinder. In addition, the structure is undesirably complicated.